Bath and method for anodic brightening of metals



United States Patent Ofi 3,203,884 Patented Aug. 31, 1965 ice corporation No Drawing. Filed Nov. '18, 1960, 'Ser. No. 70,142

Claims priority, application Germany, Nov. 20, 1959,

' 6 89 3 Ciaims. ci. 204-1405) Our invention relates to a method and bath for anodic brightening of metals and alloys, particularly unalloyed steel.

Many metals and metal alloys can be brightened by anodic treatment in mixtures of :acids. For example, chrome-nickel steel can be anodically polished in mixtures of phosphoric acid and sulfuric acid. Unalloyed carbon steel, however, cannot be satisfactorily brightened in this manner. For anodically brightening such steel it is rather necessary to use mixtures of perchloric acid and acetic acid, or the like mixed baths which must be used with particularly severe safety expedients because they involve explosion hazard if a given bath temperature is exceeded. It has also been proposed to use acid mixtures which contain chromic acid, for the purpose of anodic brightening of carbon steel, but these chromicacid mixtures rapidly change their composition during use and their regeneration is difiicult. Various types of steel, particularly chrome-nickel steels, have also been polished by using mixtures of sulfuric acid and fluoboric acid. Tests have shown that such baths can be used to some extent when employing an electrolyte according to US. Patent 2,542,779 of the following composition: 45% H 80 13% HBF (26% solution) and 42% water at 60 to 75 C. However, no polishing effect upon carbon steel could be obtained in the same bath although temperature and electric current density were It is notable that the content of fluoboric acid in the mixture can be varied Within wide limits without impairing the polishing action. For example, a very good performance was obtained With a bath content of 1.1 gram per liter of fluoboric acid, and a still good eiiect with a content of 200 grams fiuoboric acid per liter. In contrast thereto, pure phosphoric acid as well as pure fiuoboric acid are completely inelfective to produce anodic polishing.

The water content of the bath may amount to 50 to 250 grams per liter. Particularly favorable results are obtained at 150 to 200 grams per liter of water.

The anodic brightening or polishing baths according to the invention form a stable blanket of foam during electrolysis, such blanket being not observed when operating with pure phosphoric acid. The baths can be produced in a simple manner by mixing commercially available acids. For adjusting the desired water content, phosphorus pentoxide may be added if desired.

The operation of the polishing baths according to the invention is completely free of danger and not detrimental to health.

The following example relates to the anodic brightening of carbon steel without alloying constituents.

Bath constituents: 37 ml. HBF -solution of 27 B.; 0.63

liter H3PO4,

Bath concentration: 25 g./l. HBF 200 g./l. water Current density: 20 to 50 A./dm. preferably 30 to 40 A/dm.

Bath voltage: 10 volt Temperature: 20 to C., preferably 30 to 40 C.

Further examples of bath compositions and operating conditions are indicated in the table attached to this specification.

Baths according to the invention are suitable particularly for the anodic polishing of carbon steel. They are also suitable for the brightening of the other metals including chrome-nickel steel, copper, brass, aluminum and varied within wide limits. 40 light metal alloys.

Table Constitutents Bath composition in g./1. of water Current density, Temper- Polishing AJdeciature, action on H POi, d. 1.75, HBF4 Further meter 2 C. C-Steel mi. sol., 27 additions HBF4 P 0 H20 B., ml

672 560 40 30-40 None (black surface). 200 1, 070 108 40 30-40 Good.

50 1, 040 220 30-40 30-40 Very good. 25 1, 086 206 30-40 30-40 Do. 7 l, 117 196 30-40 30-40 Do. 1. 1 1, 126 193 30-10 30-40 Do. 0. 1, 127 193 30-40 30-40 Good. 0.27 1,128 193 30-40 30-40 Slight (bright veiledfi. 0. 07 1, 128 193 30-40 30-40 None.

1 Permanent foam blanket.

It is an object of our invention to provide a brightening or polishing bath which secures satisfactory results even when used for unalloyed carbon steel, Without danger of explosion or other health hazards.

We have discovered that mixtures of phosphoric acid and finoboric acid are excellently suitable for anodic polishing of carbon steel; and we have also found that such mixtures achieve an augmented brightening effect upon other metals and metal alloys at such loW processing temperatures as 30 to 40 C., for example.

2 Foaming commences.

of the bath being 150 to 200 grams per liter.

3. The method of anodically brightening carbon steel, which comprises anodically treating the steel in an electrolyte bath consisting of water-containing phosphoric acid and an addition of fiuoboric acid in an amount of l to 200 grams per liter, the water content of the bath being 50 to 250 grams per liter, at a temperature of about 30 C. to about 40 C. and a current density of about 30 to 40 amperes per square decirneter.

References Cited by the Examiner UNITED STATES PATENTS 2,108,603 2/38 Mason 204-1405 4 Bartlett 204-1405 Wiesner 204-1405 Neill 204-146 Swihart 41-42 Robinson 204-1405 DAquila 204140.5 Swagler 204-1405 Wernlund 204140.5 Satterfield 25279.3

JOHN H. MACK, Primary Examiner.

JOSEPH REBOLD, Examiner. 

1. BATH FOR ANOIDIC BRIGHTENING OF METALS AND ALLOYS, PARTICULARLY CARBON STEEL, CONSISTING OF WATER-CONTAINING PHOSPHORIC ACID AND AN ADDITION OF FLUOBORIC ACID IN AN AMOUNT OF 1 TO 200 GRAMS PER LITER, THE WATER CONTENT OF THE BATH BEING 50 TO 250 GRAMS PER LITER. 